Question 14525
Well, you need to know the midpoint formula in order to solve this. If you don't know it, I'll give it to you.
{{{(Xsub1+Xsub2)/2}}},{{{(Ysub1+Ysub2)/2}}}
Basically, you are taking the average of the 2 X values and the 2 Y values. 
Just plug those numbers into the formula.
{{{(5-2)/2}}},{{{(1+7)/2}}}
You should end up with the ordered pair
({{{3/2}}},{{{4}}})
Hope this helps!